Semiconductor device having an oxide film formed on a semiconductor substrate sidewall of an element region and on a sidewall of a gate electrode

ABSTRACT

A first isolation is formed on a semiconductor substrate, and a first element region is isolated via the first isolation. A first gate insulating film is formed on the first element region, and a first gate electrode is formed on the first gate insulating film. A second isolation is formed on the semiconductor substrate, and a second element region is isolated via the second isolation. A second gate insulating film is formed on the second element region, and a second gate electrode is formed on the second gate insulating film. A first oxide film is formed between the first isolation and the first element region. A second oxide film is formed between the second isolation and the second element region. The first isolation has a width narrower than the second isolation, and the first oxide film has a thickness thinner than the second oxide film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.11/109,763, now allowed, which is based upon and claims the benefit ofpriority from prior Japanese Patent Application No. 2005-009252, filedJan. 17, 2005, the entire contents of both of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device having an oxidefilm formed on a semiconductor substrate sidewall of an element regionand on a sidewall of a gate electrode.

2. Description of the Related Art

Several elements (transistors) forming a semiconductor device aremutually isolated via an isolation region formed on a semiconductorsubstrate. These elements each have different characteristics requiredin accordance with their functions. Moreover, the dimension of elementregion and isolation region is different in accordance with thecharacteristics.

For example, a non-volatile semiconductor memory having a two-layer gateelectrode comprising a floating gate electrode and a control gateelectrode is given as one example. In order to obtain a mass storagecapacity, a memory cell requires to micro-fabricate the foregoingelement region and isolation region as much as possible. On the otherhand, in a peripheral transistor forming a peripheral circuit fordriving the memory cell, the allowable dimension of the element regionand isolation region is determined in accordance with required electriccharacteristics. For example, a high-voltage driving transistor isformed of an element region larger than the memory cell and an isolationregion to prevent a leak current.

The following technique is employed to form the preceding memory celland peripheral circuit. According to the technique, an isolation trenchis formed, and thereafter, a semiconductor substrate sidewallfunctioning as an element region is oxidized. Etching damages caused ina semiconductor substrate are repaired when the isolation trench isformed, thereby preventing a junction leak current of impurities formedon the element region. The technique will be described below withreference to the drawings giving a NAND non-volatile memory device asone example.

FIG. 1A is a cross-sectional view showing a memory cell in the channelwidth direction. FIG. 1B is a cross-sectional view showing a peripheraltransistor in the channel width direction.

The NAND non-volatile memory device is formed according to the followingmanufacturing method. Impurity ions are implanted into a siliconsubstrate 101 to form well of memory cell, channel region 102 a, well ofperipheral transistor and channel region 102 b, and thereafter, a gateinsulating film 103 is formed. Then, a floating gate electrode of thememory cell and a first gate electrode layer consisting of polysiliconare formed on the gate insulating film 103. In this case, the first gatelayer functions as a gate electrode of peripheral and selecttransistors. Thereafter, a mask material (not shown) used for forming anisolation region is formed on the gate insulating film 103. A resistfilm protecting the element region is patterned using a lithographyprocess, and the foregoing mask material, first gate electrode layer,gate insulating film 103 and silicon substrate 101 are successivelyetched. Trenches, that is, an isolation region 107 a of the memory celland an isolation region 107 b of the peripheral transistor are formed toisolate (partition) the element region 106 a thereof and the elementregion 106 b thereof from each other.

The surface of the silicon substrate is oxidized using thermaloxidization to form silicon oxide films 108 a and 108 b. In this case,the silicon oxide film 108 a is formed on the trench surface ofisolation regions 107 a of the memory cell. The silicon oxide film 108 bis formed on the trench surface of isolation regions 107 b of theperipheral transistor. The thermal oxidization is carried out, andthereby, a sidewall of a gate electrode 104 a of the memory cell isformed with a silicon oxide film 109 a. Simultaneously, a sidewall of agate electrode 104 b of the peripheral transistor is formed with asilicon oxide film 109 b.

Thereafter, the trench functioning as the isolation region is formedwith an isolation insulating film 110, and planarized using CMP toremove the mask material. The height of the isolation insulating film110 of the memory cell is reduced using etching as the need arises toform an inter-gate insulating film 111.

A part of the inter-gate insulating film 111 is removed in theperipheral transistor and the select transistor. Thereafter, a controlgate electrode 112 a of the memory cell, that is, second gate electrodelayer is formed. In this case, the second gate electrode layer comprisesa stacked film of polysilicon and silicide. In the peripheral transistorand the select transistor, the foregoing first and second gate electrodelayers are electrically connected. Then, the gate electrode is patternedusing lithography technique, and second gate electrode, inter-gateinsulating film and first second gate electrode are successively etchedto form a gate electrode.

Thereafter, an interlayer insulating film 114 is formed, and then,source/drain diffusion layer, contact electrode 115 and interconnect 116are formed using a generally known process. In the manner as described,memory cell and peripheral transistor are formed as shown in FIG. 1A andFIG. 1B.

Silicon oxide films 108 a and 108 b formed on each sidewall of elementregions 106 a and 106 b are formed having a thickness of 4 nm using dryoxidization at temperature of 1035° C. FIG. 2A and FIG. 2B are eachenlarged views showing element regions, gate insulating film and gateelectrode in the foregoing formation.

The silicon oxide film 108 b formed on the sidewall of the elementregion 106 b has a thickness T′sb required for preventing a junctionleak current of the peripheral transistor. Even if excessive oxidizationis given to the memory cell, the silicon oxide film 108 a formed on thesidewall of the element region 106 a of the memory cell has the samethickness T′sa as T′sb. For this reason, if the scale-down of the memorycell advances, the width of the element region 106 a becomes narrow morethan the necessity in the memory cell. As a result, there is a problemthat device characteristic is worsened.

Moreover, in oxidization of the sidewall of the element region, thesidewall of the first gate electrode layer is also oxidized. The firstgate electrode is formed of polysilicon; for this reason, it is oxidizedfaster than the silicon substrate formed of single crystal silicon. As aresult, the width of a channel region controlled by the gate electrodebecomes smaller than that of the element region. The oxidized amount ofthe sidewall of the first gate electrode layer, that is, thickness T′gaand T′gb in the memory cell and the peripheral transistor are the same.Since the peripheral transistor has a large-width element region 106 b,the sidewall of the first gate electrode layer has almost no influenceby oxidization. However, the memory cell has a small-width elementregion 106 a. For this reason, the sidewall of the first gate electrodelayer is oxidized, and thereby, the width of an effective channel regionis reduced. As a result, there is a problem that device characteristicis worsened.

In oxidization of each sidewall of the silicon substrate and the gateelectrode using thermal oxidization, the oxidization rate of thepolysilicon gate electrode is faster than that of the silicon substrateformed of single crystal silicon. For this reason, the gate electrode isoxidized more than the silicon substrate. As a result, the end of thegate electrode 104 a of the memory cell is positioned inside from thatof the element region 106 a formed on the silicon substrate by L′a.Likewise, the end of the gate electrode 104 b of the peripheraltransistor is positioned inside from that of the element region 106 bformed on the silicon substrate by L′b. In this case, the foregoingdistances L′a and L′b have the same value.

In oxidization of the sidewall of the element region, an oxidizing agentdiffuses in the gate insulating film. For this reason, oxidization isgiven to the gate insulating film from the lateral direction; as aresult, a wedge-shaped oxide film is formed. The wedge-shaped oxide filmis formed in the same manner in the memory cell and the peripheraltransistor. More specifically, a horizontal distance B′sa of the formedwedge-shaped oxide film from the end of the element region 106 a of thememory cell is given. A horizontal distance B′sb of the formedwedge-shaped oxide film from the end of the element region 106 b of theperipheral transistor is given. In this case, the horizontal distanceB′sa is the same as the horizontal distance B′sb. Likewise, a horizontaldistance B′ga of the formed wedge-shaped oxide film from the end of thegate electrode 104 a of the memory cell is given. A horizontal distanceB′gb of the formed wedge-shaped oxide film from the end of the gateelectrode 104 b of the peripheral transistor is given. In this case, thehorizontal distance B′ga is the same as the horizontal distance B′gb.

Moreover, an angle θ′sa of the wedge-shaped oxide film formed at the endof the element region 106 a of the memory cell is given. An angle θ′sbof the wedge-shaped oxide film formed at the end of the element region106 b of the peripheral transistor is given. In this case, the angleθ′sa is the same as the angle θ′sb. Likewise, an angle θ′ga of thewedge-shaped oxide film formed at the end of the gate electrode 104 a ofthe memory cell is given. An angle θ′gb of the wedge-shaped oxide filmformed at the end of the gate electrode 104 b of the peripheraltransistor. In this case, the angle θ′ga is the same as the angle θ′gb.The peripheral transistor does not so receive an influence by thewedge-shaped oxide film because it has a large-width element region. Onthe contrary, the memory cell has a small-width element region; for thisreason, the wedge-shaped oxide film is formed, thereby increasing aneffective thickness of the gate insulating film. As a result, there is aproblem that device characteristic is worsened.

In order to solve the foregoing problem, the isolation regions of thememory cell and the peripheral transistor are formed separately fromeach other. By doing so, oxidization to the sidewall of the elementregion is carried out separately. However, in this case, the formationof the isolation region must be carried out two times, and this is afactor of causing the following problem. In other words, an area of theboundary for separately forming the memory cell and the peripheraltransistor increases, and the number of manufacturing processesincrease; as a result, the manufacture cast increases.

JPN. PAT. APPLN. KOKAI Publication No. 2004-186185 discloses thefollowing proposal. According to the proposal, polysilicon layer andsilicon substrate are etched to form an isolation trench. Thereafter,each exposed surface of the silicon substrate and the polysilicon layeris formed with a silicon oxide film having a thickness of 5 nm usingthermal oxidization. However, the foregoing proposal can not solve theproblem that the device characteristic of the memory cell is worsened.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided asemiconductor device comprising: a semiconductor substrate; a firstisolation region formed on the semiconductor substrate; a first elementregion isolated via the first isolation region; a first gate insulatingfilm formed on the first element region; a first gate electrode formedon the first gate insulating film; a second isolation region formed onthe semiconductor substrate; a second element region isolated via thesecond isolation region; a second gate insulating film formed on thesecond element region; a second gate electrode formed on the second gateinsulating film; a first oxide film formed between the first isolationregion and the first element region; and a second oxide film formedbetween the second isolation region and the second element region.

The first isolation region has a width narrower than the secondisolation region, and the first oxide film having a thickness thinnerthan the second oxide film.

According to another aspect of the present invention, there is provideda semiconductor device comprising: a semiconductor substrate; a firstisolation region formed on the semiconductor substrate; a first elementregion isolated via the first isolation region; a first gate insulatingfilm formed on the first element region; a first gate electrode formedon the first gate insulating film; a second isolation region formed onthe semiconductor substrate; a second element region isolated via thesecond isolation region; a second gate insulating film formed on thesecond element region; and a second gate electrode formed on the secondgate insulating film.

The first isolation region has a width narrower than the secondisolation region. The first gate electrode contacting with the firstgate insulating film has a width narrower than the first element regioncontacting with the first gate insulating film in a channel widthdirection of the first element region. The second gate electrodecontacting with the second gate insulating film has a width narrowerthan the second element region contacting with the second gateinsulating film in a channel width direction of the second elementregion. A horizontal distance from the end of the first element regionto the end of the first gate electrode in the channel width direction ofthe first element region is smaller than a horizontal distance from theend of the second element region to the end of the second gate electrodein the channel width direction of the second element region.

According to one aspect of the present invention, there is provided amethod of manufacturing a semiconductor device, comprising: forming afilm functioning as a gate insulating film and a film functioning as agate electrode on a semiconductor substrate; removing the filmfunctioning as a gate electrode, the film functioning as a gateinsulating film and the semiconductor substrate to form a firstisolation trench, and forming a first element region, a first gateinsulating film and a first gate electrode, which are isolated via thefirst isolation trench; removing the film functioning as a gateelectrode, the film functioning as a gate insulating film and thesemiconductor substrate to form a second isolation trench, and forming asecond element region, a second gate insulating film and a second gateelectrode, which are isolated via the second isolation trench; andforming a first oxide film on a sidewall of the first element regionwhile forming a second oxide film on a sidewall of the second elementregion. The first isolation trench has a width narrower than the secondisolation trench, and the first oxide film has a thickness thinner thanthe second oxide film.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A and FIG. 1B are cross-sectional views showing a conventionalsemiconductor device;

FIG. 2A and FIG. 2B are enlarged views showing a portion stacked withelement region, gate insulating film and gate electrode in thesemiconductor device shown in FIG. 1A and FIG. 1B;

FIG. 3A and FIG. 3B are top plan views showing the configuration of asemiconductor device according to an embodiment of the presentinvention;

FIG. 4A and FIG. 4B are cross-sectional views taken along lines A-A andB-B respectively in the semiconductor device of the embodiment;

FIG. 5A and FIG. 5B are enlarged views showing a portion stacked withelement region, gate insulating film and gate electrode in thesemiconductor device shown in FIG. 4A and FIG. 4B;

FIG. 6A and FIG. 6B are cross-sectional views to explain a first processof the method of manufacturing the semiconductor device of theembodiment;

FIG. 7A and FIG. 7B are cross-sectional views to explain a secondprocess of the method of manufacturing the semiconductor device of theembodiment;

FIG. 8A and FIG. 8B are cross-sectional views to explain a third processof the method of manufacturing the semiconductor device of theembodiment;

FIG. 9A and FIG. 9B are cross-sectional views to explain a fourthprocess of the method of manufacturing the semiconductor device of theembodiment;

FIG. 10A and FIG. 10B are cross-sectional views to explain a fifthprocess of the method of manufacturing the semiconductor device of theembodiment;

FIG. 11A and FIG. 11B are cross-sectional views to explain a sixthprocess of the method of manufacturing the semiconductor device of theembodiment; and

FIG. 12A and FIG. 12B are cross-sectional views to explain a seventhprocess of the method of manufacturing the semiconductor device of theembodiment.

DETAILED DESCRIPTION OF THE INVENTION

A semiconductor device according to an embodiment of the presentinvention and a method of manufacturing the same device will bedescribed below with reference to the accompanying drawings. In thefollowing description, the same reference numerals are used to designateportions common to all drawings.

According to the embodiment, a memory cell of a NAND non-volatilesemiconductor memory is given as an example in which an isolation regionwidth is narrow while a peripheral transistor thereof is given as anexample in which it is wide. The foregoing memory cell and peripheraltransistor will be explained with reference to FIG. 3A and FIG. 3B toFIG. 12A and FIG. 12B. The peripheral transistor forms a circuitrequired for data write and read to the memory cell, and is formed onthe same semiconductor substrate as the memory cell.

FIG. 3A is a top plan view showing a memory cell array of the NANDnon-volatile semiconductor memory of the present invention. FIG. 3B is atop plan view showing a peripheral transistor of the NAND non-volatilesemiconductor memory.

As shown in FIG. 3A, element regions 6 a isolated via isolation regions7 a are formed on a silicon semiconductor substrate. Each NAND cell unithas the configuration that series-connected several memory cells MC anda select transistor ST are formed on the element region 6 a. The selecttransistor ST is connected to one end of series-connected several memorycells MC. Memory cells MC arrayed in the direction of a word line 12 ahave their gates connected via a common word line (control gateelectrode) 12 a. Select transistors ST have their gates connected via acommon select gate line 12 a′. One end of a current path of each selecttransistor ST is connected with a bit line 16 a via a bit line contact15 a.

As illustrated in FIG. 3B, the peripheral transistor is formed on anelement region 6 b above the same silicon semiconductor substrate formedwith the memory cells. The peripheral transistor has gate electrode 12b, and source/drain region formed on the element region 6 b. The gateelectrode 12 b is connected with interconnection 16 for making aconnection between elements (peripheral transistors) via an electricallyconnected contact electrode 15. The element region 6 b is isolated viaan isolation region 7 b.

FIG. 4A is a cross-section view taken along a line A-A of the memorycell array shown in FIG. 3A. FIG. 4B is a cross-section view taken alonga line B-B of the peripheral transistor shown in FIG. 3B.

The structure of the memory cell array shown in FIG. 4A will bedescribed below.

A well/channel region 2 a is formed above a silicon semiconductorsubstrate 1. The well/channel region 2 a is formed with a projectedelement region 6 a. Several element regions 6 a are arrayed with apredetermined interval. An isolation region 7 a is formed between theelement regions 6 a. The isolation region 7 a is formed in a manner thatan insulating film such as silicon oxide film and silicon nitride filmis buried in an isolation trench formed between the element regions 6 a.In this embodiment, a silicon oxide film is buried therein. Moreover, asilicon oxide film 8 a is formed between the element region 6 a and theisolation region 7 a. In other words, the sidewall of the element region6 a is formed with the silicon oxide film 8 a.

A gate insulating film 3 a is formed on the element region 6 a. A gateelectrode 4 a is formed on the gate insulating film 3 a. The side of thegate electrode 4 a is formed with a silicon oxide film 9 a.

An inter-gate insulating film 11 is formed on the gate electrode 4 a andthe isolation region 7 a. A control gate electrode 12 a is formed on theinter-gate insulating film 11. Moreover, an interlayer insulating film14 is formed on the control gate electrode 12 a. A bit line 16 a isformed on the interlayer insulating film 14.

The structure of the peripheral transistor shown in FIG. 4B will bedescribed below.

A well/channel region 2 b is formed above a silicon semiconductorsubstrate 1. The well/channel region 2 b is formed with a projectedelement region 6 b. Several element regions 6 b are arrayed with apredetermined interval. An isolation region 7 b is formed between theelement regions 6 b. The isolation region 7 b is formed in a manner thatan insulating film such as silicon oxide film and silicon nitride filmis buried in an isolation trench formed between the element regions 6 b.In this embodiment, a silicon oxide film is buried therein. Moreover, asilicon oxide film 8 b is formed between the element region 6 b and theisolation region 7 b. In other words, the sidewall of the element region6 b is formed with the silicon oxide film 8 b.

In this case, the element region 6 a of the memory cell has a width(channel-width direction length) smaller than the element region 6 b ofthe peripheral transistor. The isolation region 7 a of the memory cellhas a width (channel-width direction length) smaller than the isolationregion 7 b of the peripheral transistor. For example, the width of theisolation region 7 a of the memory cell is less than 0.1 μm while thewidth of the isolation region 7 b of the peripheral transistor is morethan 1 μm. The silicon oxide film 8 a formed at the sidewall of theelement region 6 a of the memory cell is formed thinner than the siliconoxide film 8 b formed at the sidewall of the element region 6 b of theperipheral transistor.

A gate insulating film 3 b is formed on the element region 6 b. A gateelectrode 4 b is formed on the gate insulating film 3 b. The side of thegate electrode 4 b is formed with a silicon oxide film 9 b. The siliconoxide film 9 a formed at the sidewall of gate electrode 4 a of thememory cell is formed thinner than the silicon oxide film 9 b formed atthe sidewall of the gate electrode 4 b of the peripheral transistor.

An inter-gate insulating film 11 is formed on the gate electrode 4 b andthe isolation region 7 b. In this case, a part of the inter-gateinsulating film 11 formed on the gate electrode 4 b and the isolationregion 7 b is removed. A gate electrode 12 b formed of the same film asthe control gate electrode 12 a is formed on the inter-gate insulatingfilm 11 and the gate electrode 4 b having the partially removedinter-gate insulating film 11. Moreover, an interlayer insulating film14 is formed on the control gate electrode 12 a. An interconnect(wiring) 16 is formed on the interlayer insulating film 14. Theinterconnect 16 is electrically connected to the gate electrode 12 b viaa contact electrode 15 formed in the interlayer insulating film 14.

In the memory cell shown in FIG. 4A and the peripheral transistor shownin FIG. 4B, the silicon substrate 1 is etched to form the isolationtrench in order to form isolation regions 7 a and 7 b. The isolationtrench is formed using RIE (Reactive Ion Etching); for this reason,damage occurs in the silicon substrate 1. Thermal oxidization is carriedout to recovery the damage occurring in the silicon substrate 1, andthereby, silicon oxide films 8 a and 8 b are formed. Therefore, anamount of oxidization increases resulting from thermal oxidization, andthereby, damage is sufficiently recovered while the silicon substrate 1is further oxidized. As a result, the width of the element region isreduced.

The non-volatile semiconductor memory of this embodiment has thestructure given below. That is, the silicon oxide film 8 a formed at thesidewall of the element region 6 a of the memory cell is formed thinnerthan the silicon oxide film 8 b formed at the sidewall of the elementregion 6 b of the peripheral transistor. By doing so, it is possible toincrease an amount of oxidization for recovering the damage, and to makethin the silicon oxide film 8 a even if the silicon oxide film 8 b isformed thicker. In order to drive high voltage, the peripheraltransistor has a need to make small a junction leak current between thesource/drain diffusion region and the well/channel region on the siliconsubstrate 1. Therefore, the foregoing structure serves to sufficientlyrecover etching damage in the peripheral transistor. On the other hand,high voltage is not applied to the memory cell more than the peripheraltransistor; thus, the damage may be recovered by the necessary minimum.In the memory cell, an operation is required in the micro-fabricatedelement region 6 a. Thus, the amount of oxidization of the sidewall ofthe element region 6 a is reduced, thereby preventing the width of theelement region 6 a from being narrowed. Therefore, high-performancedevice characteristic is obtained. On the other hand, the peripheraltransistor has a sufficiently wide element region width capable ofdisregarding the amount of oxidization of the sidewall of the elementregion 6 a. Thus, there is no problem even if the amount of oxidizationof the sidewall of the element region 6 a is increased more than thememory cell.

The non-volatile semiconductor memory of this embodiment is manufacturedusing the following method in order to prevent parasitic transistor(corner transistor) from being formed at the corner of the elementregion. As depicted in FIG. 6A and FIG. 6B, a first polysilicon gateelectrode layer 4 is formed on the gate insulating film above thesilicon substrate 1. The gate electrode layer 4 functions as a floatinggate electrode of the memory cell and a gate electrode of the peripheraland select transistors. A mask material 5 used for etching the isolationtrench is formed on the first gate electrode layer 4. A resist film forprotecting the element region is patterned and formed on the maskmaterial 5 using lithography process. Then, mask material 5, first gateelectrode layer 4, gate insulating film 3 and silicon substrate 1 aresuccessively etched to form the isolation trench for forming anisolation region in the silicon substrate 1. Thereafter, thermaloxidization is carried out so that the sidewall of the element region isformed with a silicon oxide film. When the silicon substrate 1 of theelement region is oxidized, the side of the first gate electrode layer 4is also oxidized. As described before, the foregoing mask material 5,first gate electrode layer 4, gate insulating film 3 and siliconsubstrate 1 are etched via one-time etching process. By doing so, it ispossible to prevent misalignment between the element region 6 a and thefloating gate electrode 4 a and misalignment between the element region6 b and the gate electrode 4 b, as seen from FIG. 7 a and FIG. 7B. Thiscontributes to preventing the disadvantage described below. That is,misalignment occurs between the element region and the gate electrode;for this reason, the gate electrode gives an influence to the sidewallof the element region. As a result, a parasitic transistor is formed atthe corner of the element region.

Moreover, the non-volatile semiconductor memory of this embodiment hasthe structure given below. That is, the silicon oxide film 9 a formed atthe sidewall of the gate electrode 4 a of the memory cell is formedthinner than the silicon oxide film 9 b formed at the sidewall of thegate electrode 4 b of the peripheral transistor. By doing so, it ispossible to recover etching damage required for making small a junctionleak current of the peripheral transistor. Simultaneously, the siliconoxide film 9 a formed at the sidewall of the gate electrode 4 a of thememory cell is formed thinner. As a result, it is possible to prevent areduction of effective channel width determined depending on the gateelectrode width of micro-dimension memory cell, and to obtain highdevice characteristic. On the other hand, the peripheral transistor hasa sufficiently wide element region width capable of disregarding theamount of oxidization of the sidewall of the gate electrode 4 b. Thus,there is no problem even if the amount of oxidization of the sidewall ofthe gate electrode 4 b is increased more than the memory cell.

FIG. 5A is an enlarged view showing a portion stacked with elementregion 6 a, gate insulating film 3 a and gate electrode 4 a in thememory cell shown in FIG. 4A. FIG. 5B is an enlarged view showing aportion stacked with element region 6 b, gate insulating film 3 b andgate electrode 4 b in the peripheral transistor shown in FIG. 4B.

The silicon oxide film 8 a formed at the sidewall of the element region6 a of the memory cell is formed thinner than the silicon oxide film 8 bformed at the sidewall of the element region 6 b of the peripheraltransistor. In other words, the silicon oxide film 8 a has a thicknessTsa thinner than a thickness Tsb of the silicon oxide film 8 b. Thesilicon oxide film 9 a formed at the sidewall of the gate electrode 4 aof the memory cell is formed thinner than the silicon oxide film 9 bformed at the sidewall of the gate electrode 4 b of the peripheraltransistor. In other words, the silicon oxide film 9 a has a thicknessTga thinner than a thickness Tgb of the silicon oxide film 9 b.

The sidewalls of the element region (silicon substrate) and the gateelectrode are oxidized using thermal oxidization. In this case, theoxidization rate of the polysilicon gate electrode is faster than thatof the element region formed of single crystal silicon. Therefore, thesidewall of the gate electrode is oxidized more than that of the elementregion. The end of the gate electrode 4 a of the memory cell ispositioned inside from the end of the element region 6 a by a distanceLa. Likewise, the end of the gate electrode 4 b of the peripheraltransistor is positioned inside from the end of the element region 6 bby a distance Lb.

A ratio of the oxidization rate of polysilicon to single crystal silicondoes not depend on the width of the isolation region. However, the widthof the isolation region is narrow; therefore, oxidization is restrained.As a result, the distance La has a value smaller than the distance Lb.The foregoing features is used, and thereby, the sidewalls of elementregions 6 a and 6 b are respectively formed with silicon oxide films 8 aand 8 b so that a recess is formed in the isolation trench formed withthe isolation region, as shown in FIG. 5A and FIG. 5B. Thereafter, thefollowing structure is given, that is, the isolation trench is fullyfilled with the silicon oxide film 10. By doing so, the followingprediction is given even if it is difficult to measure each thickness ofsilicon oxide films 8 a and 8 b formed at the sidewalls of the elementregions. Namely, the silicon oxide film 8 a of the memory cell has thethickness Tsa thinner than the thickness Tsb of the silicon oxide film 8a of the peripheral transistor.

In the non-volatile semiconductor memory of this embodiment, the endportion of the gate insulating film 3 a of the memory cell is formedwith wedge-shaped oxide films 8 sa and 9 ga as shown in FIG. 5A. On theother hand, the end portion of the gate insulating film 3 b of theperipheral transistor is formed with wedge-shaped oxide films 8 sb and 9gb as shown in FIG. 5B. In this case, the wedge-shaped oxide films 8Saand 9 ga are formed smaller than wedge-shaped oxide films 8Sb and 9 gb.In other words, a horizontal distance Bsa of the formed wedge-shapedoxide film 8 sa from the end of the element region 6 a of the memorycell is given. A horizontal distance Bsb of the formed wedge-shapedoxide film 8 sb from the end of the element region 6 b of the peripheraltransistor is given. In this case, the horizontal distance Bsa issmaller than the horizontal distance Bsb. Likewise, a horizontaldistance Bga of the formed wedge-shaped oxide film 8 sa from the end ofthe gate electrode 4 a of the memory cell is given. A horizontaldistance Bgb of the formed wedge-shaped oxide film 8 sb from the end ofthe gate electrode 4 b of the peripheral transistor is given. In thiscase, the horizontal distance Bga is smaller than the horizontaldistance Bgb. Moreover, an angle θsa of the wedge-shaped oxide film 8 saformed at the end of the element region 6 a of the memory cell is given.An angle θsb of the wedge-shaped oxide film 8 sb formed at the end ofthe element region 6 b of the peripheral transistor is given. In thiscase, the angle θsa is smaller than the angle θsb. Likewise, an angleθga of the wedge-shaped oxide film 9 ga formed at the end of the gateelectrode 4 a of the memory cell is given. An angle θgb of thewedge-shaped oxide film 9 gb formed at the end of the gate electrode 4 bof the peripheral transistor is given. In this case, the angle θga issmaller than the angle θgb.

As described above, the wedge-shaped oxide films 8 sa (or 9 ga) formedon the gate insulating film 3 a of the memory cell is smaller than thewedge-shaped oxide films 8 sb (or 9 gb) formed on the gate insulatingfilm 3 b of the peripheral transistor. Therefore, it is possible torestrain an increase of the effective film thickness of the gateinsulating film 3 a of the memory cell having micro channel regionwidth, and to obtain high device characteristic. On the other hand, theperipheral transistor has a sufficiently wide channel region widthcapable of disregarding the area of the wedge-shaped oxide film formedat the gate insulating film 3 b. Therefore, there is no problem even ifthe gate insulating film 3 b is formed with a wedge-shaped oxide filmlarger than the wedge-shaped oxide film formed of the memory cell.

Both horizontal distance and angle θf each wedge-shaped oxide filmformed at the gate insulating films 3 a and 3 b do not always satisfythe relationship described above. The memory cell can obtain high devicecharacteristic so long as one of the horizontal distance and anglesatisfies the relationship described above.

In the semiconductor device of the embodiment, oxidization issufficiently carried out with respect to the peripheral transistor inorder to prevent a junction leak current, and thereby, etching damage isrecovered. Simultaneously, necessary oxidization is only carried outwith respect to the memory cell. By doing so, it is possible to preventdevice characteristic from being worsened resulting from a reduction ofthe element region width of the memory cell.

The method of manufacturing the non-volatile semiconductor deviceaccording to the embodiment will be described below with reference toFIG. 4A, FIG. 4B and FIG. 6A, FIG. 6B to FIG. 12A and FIG. 12B. FIG. 4Aand FIG. 6A to FIG. 12A show a cross-sectional view of the memory cell.FIG. 4B and FIG. 6B to FIG. 12B show a cross-sectional view of theperipheral transistor.

As shown in FIG. 6A and FIG. 6B, well/channel region 2 a of the memorycell and well/channel region 2 b of the peripheral transistor are formedin the silicon semiconductor substrate 1 using ion implantation. Thesurface of the silicon substrate 1 is formed with a gate insulating film(e.g., silicon oxide film) 3 of the foregoing memory cell and peripheraltransistor. Thereafter, a first gate electrode layer (e.g., polysilicon)4 is formed on the gate insulating film 3. The first gate electrodelayer functions as a gate electrode of the memory cell, and as a part ofa gate electrode of the peripheral electrode. A silicon nitride film 5is further formed on the first gate electrode layer 4. The siliconnitride film 5 is used as a mask material for etching an isolationtrench formed with an isolation region.

Then, a resist film is patterned using lithography process to protectelement regions. As illustrated in FIG. 7A and FIG. 7B, the foregoingmask material 5, first gate electrode layer 4, gate insulating film 3and silicon substrate 1 are successively etched using RIE. By doing so,the silicon substrate 1 is formed with each isolation trench for formingisolation regions 7 a and 7 b of the memory cell and the peripheraltransistor. The isolation region 7 a and 7 b isolates an element region6 a of the memory cell and an element region 6 b of the peripheraltransistor, respectively. In this case, the element region 6 a of thememory cell has a width smaller than the element region 6 b of theperipheral transistor. Moreover, the isolation region 7 a of the memorycell has a width smaller than the isolation region 7 b of the peripheraltransistor. For example, the isolation region 7 a of the memory cell hasa width of 0.1 μm or less while the isolation region 7 b of theperipheral transistor has a width of 1 μm or more.

As depicted in FIG. 8A and FIG. 8B, the surface of the silicon substrateis oxidized using thermal oxidization. By doing so, the surface of theisolation trench formed with the isolation region 7 a of the siliconsubstrate 1 is formed with a silicon oxide film 8 a. On the other hand,the surface of the isolation trench formed with the isolation region 7 bof the silicon substrate 1 is formed with a silicon oxide film 8 b. Bythe thermal oxidization, the sidewall of the gate electrode 4 a of thememory cell is formed with a silicon oxide film 9 a while the sidewallof the gate electrode 4 b of the peripheral transistor is formed with asilicon oxide film 9 b.

In this case, oxidization using radical oxygen is carried out as thethermal oxidization, and thereby, the following advantage is obtained.The silicon oxide film 8 a formed at the sidewall of the memory cellelement region 6 a is formed thinner than the silicon oxide film 8 bformed at the sidewall of the peripheral transistor element region 6 b.Because the isolation region 7 a has a small width while the isolationregion 7 b has a large width. Moreover, the silicon oxide film 9 aformed at the sidewall of the gate electrode 4 a of the memory cell isformed thinner than the silicon oxide film 9 b formed at the sidewall ofthe gate electrode 4 b of the peripheral transistor. This is based onthe following reason. More specifically, the amount of oxidization ofthe each sidewall of element region and gate electrode depends on theisolation region width. The amount of oxidization is a little in thememory cell because the isolation region 7 a has a small width, while itis much in the peripheral transistor because the isolation region 7 bhas a large width.

For example, oxidization using radical oxygen is carried out under theconditions described below.

Oxidization atmosphere: Ar/H₂/0₂=500/5/5 sccm.

Pressure: 133.33 Pa

Treatment temperature: 600° C.

Oxidization time: 40 sec.

By doing so, the sidewall of the element region 6 a of the memory cellis formed with a silicon oxide film 8 a of 2 nm while the sidewall ofthe gate electrode 4 a thereof is formed with a silicon oxide film 9 aof 2.4 nm. Concurrently, the sidewall of the element region 6 a of theperipheral transistor is formed with a silicon oxide film 8 b of 4 nmwhile the sidewall of the gate electrode 4 b thereof is formed with asilicon oxide film 8 a of 4.8 nm.

The foregoing oxidization using radical oxygen is carried out, andthereby, silicon oxide films 8 a and 8 b are simultaneously formed viaone-time oxidization process. More specifically, the sidewall of theelement region 6 a of the memory cell is formed with a thin siliconoxide film 8 a. Simultaneously, the sidewall of the element region 6 bof the peripheral transistor is formed with a thin silicon oxide film 8b thicker than the silicon oxide film 8 a. Therefore, there is no needof forming the isolation region separately from the memory cell and theperipheral transistor. In addition, each sidewall of the element regionsis formed with silicon oxide film having different thickness.Consequently, this serves to reduce the manufacturing cost.

An isolation insulating film (e.g., silicon oxide film) 10 is formed inisolation trenches formed with isolation regions 7 a and 7 b, and then,planarized using CMP. Thereafter, the mask material 5 is removed. Asseen from FIG. 9A and FIG. 9B, the isolation insulating film 10 of thememory cell is etched to reduce the height as the need arises, therebyforming an inter-gate insulating film 11.

As shown in FIG. 10B, part of the gate insulating film 11 is removed inthe peripheral transistor, and simultaneously, the same as above isremoved in the select transistor although not shown. As illustrated inFIG. 10A and FIG. 10B, a control gate electrode of the memory cell, thatis, second gate electrode layer 12 comprising a stacked film ofpolysilicon and silicide is formed. In this case, the first gateelectrode layer and the second gate electrode layer 12 are electricallyconnected in the peripheral transistor and the select transistor.

A resist film for protecting a gate electrode is patterned and formed onthe second gate electrode layer 12 using lithography process. Theforegoing second gate electrode layer 12, inter-gate insulating film 11,first gate electrode layers 4 a and 4 b are successively etched. Bydoing so, the following gate electrodes are formed as seen from FIG. 11Aand FIG. 11B. The gate electrodes are floating gate electrode 4 a andcontrol gate electrode 12 a of the memory cell, gate electrodes 4 a′ and12 a′ of the select transistor, gate electrodes 4 b and 12 b of theperipheral transistor. FIG. 11A and FIG. 11B each show cross-sectionalviews in the direction perpendicular to the cross sections shown in FIG.10A and FIG. 10B.

As depicted in FIG. 12A and FIG. 12B, the gate insulating film isthermally oxidized as a need arises. Source/drain diffusion layer 13,interlayer insulating film 14, contact electrode 15, bit line contactelectrode 15 a, interconnect 16 and bit line 16 a are formed using agenerally known process. The memory cell and the peripheral transistorare manufactured via the processes described above. Incidentally, FIG.4A and FIG. 4B are cross-sectional views including the gate electrode inthe direction perpendicular to FIG. 12A and FIG. 12B.

Thereafter, upper interconnect layers are further formed using agenerally known process, and thus, a non-volatile semiconductor memoryis manufactured.

According to the manufacturing method described above, the isolationtrench is formed, and thereafter, the semiconductor substrate sidewallfunctioning as the element region is oxidized to recover etchingdamages. The foregoing process is carried out via thermal oxidizationusing radical oxygen. By doing so, the oxide film formed at the elementregion sidewall of the memory cell is formed thinner than the oxide filmformed at the element region sidewall of the peripheral transistor.Because the memory cell has a narrow isolation region width (distancebetween element regions is small) while the peripheral transistor has awide isolation region width (distance between element regions is large).

According to the foregoing thermal oxidization using radical oxygen, theoxide film formed at the element region sidewall of the memory cell isformed thinner than that of the peripheral transistor via one-timeoxidization process. Therefore, it is possible to prevent deteriorationof device characteristic of the memory cell without increasing themanufacturing cost. More specifically, the isolation regions of thememory cell and the peripheral transistor are separately formed. Theoxide film formed at the element region sidewall of the memory cell isformed thinner than that of the peripheral transistor via the sameoxidization process without separately oxidizing element regionsidewalls. Thus, it is possible to prevent an increase of themanufacturing cost resulting from an increase of the number ofprocesses. In addition, it is possible to prevent deterioration ofdevice characteristic of the memory cell resulting from a reduction ofthe element region width of the memory cell.

According to the manufacturing method of the present embodiment, thefollowing structure is given via one-time oxidization process. That is,the oxide film formed at the element region sidewall of the memory cellis formed thinner than that of the peripheral transistor. Therefore, itis possible to prevent deterioration of device characteristic of thememory cell without increasing the manufacturing cost.

In the embodiment, the isolation region is formed using the gateinsulating film and part of the gate electrode as a mask. Oxidizationusing radical oxygen described in the embodiment may be used in the casewhere gate insulating film and gate electrode are formed after theisolation region is formed. In also case, the effect of the presentinvention is obtained. That is, a silicon oxide film formed at theelement region sidewall of the memory cell having a narrow isolationregion width is formed thinner than that of the peripheral transistorhaving a wide isolation region width.

According to the embodiment of the present invention, in order torestrain a junction leak current, sufficient oxidization is carried outwith respect to the peripheral transistor, and thereby, etching damagesare recovered. Simultaneously, necessary oxidization is only carried outwith respect to the memory cell. Therefore, it is possible to provide asemiconductor device, which can prevent deterioration of devicecharacteristic of the memory cell resulting from a reduction of theelement region width of the memory cell. Moreover, the followingstructure is given via one-time oxidization process. That is, the oxidefilm formed at the element region sidewall of the memory cell is formedthinner than that of the peripheral transistor. Therefore, it ispossible to provide a method of manufacturing a semiconductor device,which can achieve the foregoing object without increasing themanufacturing cost.

The present invention is not limited to the foregoing embodiment, andthe configuration is changed or added, and thereby, various embodimentsmay be provided.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A method of manufacturing a semiconductor device, comprising: forminga first film and a second film on a semiconductor substrate; removingthe second film, the first film and the semiconductor substrate to forma first isolation trench, and forming a first element region, a firstgate insulating film and a first gate electrode, which are isolated viathe first isolation trench; removing the second film, the first film andthe semiconductor substrate to form a second isolation trench, andforming a second element region, a second gate insulating film and asecond gate electrode, which are isolated via the second isolationtrench; and forming a first oxide film on a sidewall of the firstelement region while forming a second oxide film on a sidewall of thesecond element region, wherein the first isolation trench has a widthnarrower than the second isolation trench, the first oxide film has athickness thinner than the second oxide film, the first gate electrodecontacting with the first gate insulating film has a width narrower thanthe first element region contacting with the first gate insulating filmin a channel width direction of the first element region, and the secondgate electrode contacting with the second gate insulating film has awidth narrower than the second element region contacting with the secondgate insulating film in a channel width direction of the second elementregion.
 2. The method according to claim 1, wherein the first and secondisolation trenches are formed via the same process.
 3. The methodaccording to claim 1, wherein the first and second oxide films areformed via the same process.
 4. The method according to claim 3, whereinthe first and second oxide films are formed in an atmosphere containingradical oxygen.
 5. The method according to claim 1, further comprising:forming a control gate electrode on the first gate electrode with aninsulating film interposed between the control gate electrode and thefirst gate electrode, wherein the first gate electrode is a floatinggate electrode.